I noticed there is no space between the value and the string "dbpurgeage" in the output.

Looks intentional to me:

86400seconds is the same than 86400s or 24hours (24h) or 1440min or 1days (or 1d).

See https://manpages.debian.org/bookworm/fail2ban/jail.conf.5.en.html#TIME_ABBREVIATION_FORMAT

While preparing the patch, I noticed the apostrophe ` at the beginning of the line which seems out of place.

It is also intentional (historic), in this way it would show fail2ban (and its tools) output several blocks:

Results
=======

Prefregex: 1 total
|  ...
`-

Failregex: 1 total
|-  #) [# of hits] regular expression
|  23) [1] ...
`-

Date template hits:
|- [# of hits] date format
|  [1] {^LN-BEG}Day(?P<_sep>[-/])Month(?P=_sep)(?:ExYear|ExYear2) %k:Minute:Second
`-

However questionable and maybe doesn't make sense for single parameter.

But because it is historic (and can be parsed by some tools or user-side scripts), I don't think it is good idea to change the behavior of beautifier output. At least not before next major release.